Agglomeration of particulate metals

ABSTRACT

Very finely divided metal particles are agglomerated in a fluidized bed to useful larger sizes by coking heavy hydrocarbons in the bed at 850* to 1,100* F.

United States Patent William J. Metrailer East Baton Rouge, La.

Dec. 11, 1968 Sept. 21, 1971 Esso Research and Engineering Company inventor Appl. No. Filed Patented Assignee AGGLOMERATION 0F PARTICULATE METALS 10 Claims, 1 Drawing Fig.

[56] References Cited UNITED STATES PATENTS 912,641 2/1909 Atcherson et a1 75/25 2,014,044 9/1935 l-laswell 75/25 X 3,231,366 l/l966 Schenck et al... 75/26 3,356,488 l2/l967 Walsh 75/26 X 3,414,402 12/1968 Volk etal..... 75/26 3,420,656 1/1969 Mekler et aL. 75/4 X 3,428,446 2/l969 Locke, Jr 75/26 Primary Examiner-Allen B. Curtis Anorne \'-Manahan and Wright ABSTRACT: Very finely divided metal particles are agglomerated in a fluidized bed to useful larger sizes by coking heavy hydrocarbons in the bed at 850 to 1,100 F.

PATENTEDSEPZI ISYI 3507.217

IRON ORE- REACTOR /2 m 2 REDUCING GAS l 7 V 24 :a-HYDRQC LIQUID AGGLOM ERATOR FLUIDIZING GAS W/dlwm Mahala Inventor AGGLOMERATION OF PARTICULATE METALS BACKGROUND OF THE INVENTION This invention relates to the preparation of particulate metals for use in steel-making processes. More particularly, it relates to the preparation of reduced iron ore particles in suitable size ranges for use in steel-making processes.

It is known to prepare metals in finely divided particulate form. It has recently become of increased interest to prepare reduced iron ore particles by the direct reduction of oxidic iron ores. In such processes, the metallic iron particles are produced by subjecting finely ground iron ore .at relatively high temperatures up to just below the softening pointof the ore to direct contact with hot reducing gases.

In a typical such process, the particulate ore is fluidized in a bed, or series of beds, and reduced by contact with ascending reducing gases such as carbon monoxide, hydrogen, light hydrocarbons such as methane, or mixtures of these and other gases. The ores, to be suitable for reduction in a fluidized process, must be finely ground to fluidizable size ranges, i.e., ranging generally in average particle sizes from about 50 to about 400 microns. To obtainfluidizable size ranges, fresh ore is ground in conventional mills, such as ball mills, hammer mills and the like, until the average particle size is within the desired range. However, in grinding the ores, substantial amounts of particles are produced having sizes below 50 microns, and many particles range down as low as 10 microns, or even lower. After the reduction is completed, the very fine reduced iron, i.e., the fraction ranging less than about 325 mesh (Tyler sieve series), presents considerable difficulties. These very fine particles are highly susceptible to back-oxidation upon contact with the atmosphere. Furthermore, they are very easily entrained, and consequently they present pollution problems when they are stored outdoors. Also, when feeding the reduced iron product to a steel-making process, the very finely divided particles, less than about 325 mesh in size, may tend to form a dust cloud when attempts are made to inject them into a bath of molten metal. This results in the loss of a substantial portion of the material.

Since the very fine particles, less than about 325 mesh in size, often comprise as much as 20 percent, and sometimes as much as 50 percent, of the total reduced ore product, the difficulties and expenses involved in their back-oxidation or loss are considerable. Accordingly, it would be extremely desirable to develop a method for handling reduced ore particles while lessening the back-oxidation or loss of the most finely divided particles. It is the primary objective of this invention to devise such a method.

SUMMARY OF THE INVENTION This invention contemplates providing a fluidized bed of metal particles having fluidizable sizes ranging from about I to about 10,000 microns, averaging about 50 to about 400 microns and containing a substantial fractionof particles ranging less than about 325 mesh in size, maintaining the bed at temperatures ranging from about 850 F. to about l,l F preferably from about 900 F. to about l,000 F., introducing into the bed a heavy liquid hydrocarbon containing at least about weight percent Conradson carbon content, preferably at least about weight percent Conradson carbon, and coking the hydrocarbon in the bed to agglomerate the finely divided metal particles into substantially larger particles.

The heavy liquid hydrocarbons suitable for use in this invention include any conventional petroleum or coal-type heavy hydrocarbons having at least l0 weight percent Conradson carbon (as to Conradson carbon content, see ASTM Test D-l89-5. Typical of the hydrocarbons suitable for use are the high carbon steam-cracked tars, coal tar pitches, and atmospheric and vacuum residuums from petroleum, an the like. In general, the higher the carbon content, the better the hydrocarbon for use in the present invention, provided the hydrocarbon can be liquified at the fluid bed conditions,. The

bed of particles is fluidized by a stream of gas at superficial gas velocities of about 0.3 to 1.5 feet per second, preferably about 0.5 to L0 feet per second. The fluidizing gas can be an inert gas such as nitrogen or steam or it can be a reducing gas such as a hydrocarbon gas or hydrogen or carbon monoxide. In general, anyconvenient nonoxidizing gases can be used. Since the heavy liquid hydrocarbons which are injected into the fluid bed liberate light gaseous hydrocarbons and hydrogen upon coking, they can contribute to the fluidizing gas. Thus, if the heavy liquid hydrocarbon is introduced into the lower por-v tion of the fluidized bed, upon cracking it generates substantial quantities of gases which will aid in the fluidization of the bed and thus minimize the requirements for added fluidizing gases. It is preferable, however, to introduce the heavy liquid hydrocarbon into the upper portion or on top of the fluid bed, since there is a tendency in the fluidized bed for the very finely divided metal particles to congregate at the top of the bed while the larger particles tend to concentrate at the bottom. Accordingly, more efficient agglomeration of the very finely divided particles is achieved when the heavy hydrocarbon is sprayed or otherwise added to the top of the bed.

The use of too finely divided droplets of heavy hydrocarbon is to be avoided. When the droplets are too small there is a tendency for them to form thin layers of carbon on each of the metal particles without significant agglomeration of the very fine particles. In general, the droplets should average at least about 1/10 the size of the largest particle for which agglomeration one-tenth desired and can range up to average droplet sizes of about 10 times the size of the average metal particle in the fluid bed. Too-large droplets, may however, cause loss of fluidization.

When the heavy hydrocarbons are introduced into the bed of fluidized metal particles at the conditions described above, the particles less than about 325 mesh in size are agglomerated to form aggregates which are bound together by the coke formed upon the partial coking of the hydrocarbons. Thus, when the conditions of temperature, hydrocarbon feed rate, and fluidizing gas velocity are properly controlled, the fluidized particles are cemented together by the heavy, sticky residue produced in the course of the partial coking of the heavy hydrocarbon to from stable attrition resistant aggregates which further harden as the coking of the residue proceeds. The increase in size obtainable by the particle agglomeration in accordance with this invention may range as high as 10-100 times the size of the original fines and permits the production of metal particle aggregates of up to about A- inch diameter depending upon the amount of carbon deposited.

Specific reaction conditions suitable for use in this invention depend to some extent upon the particular heavy hydrocarbon used and the amount of particles present in sizes less than 325 mesh. In general, temperatures ranging from about 850-l,l00 F. produce sticky cementing residues for most feeds within relatively short times and are therefore preferred. Too-high temperatures result in violent cracking which inhibits agglomeration and suppresses the formation of sticky excessive stickiness which cause defluidization or bogging of the fluid bed.

In order to provide sufficient proportions of sticky residue the heavy hydrocarbon liquid feed rate should be sufficient to adequately coat the finely divided particles without defluidizing the fluid bed. Generally, feed rates of about 0.1-1.0 parts by weight of liquid hydrocarbon per hour per weight of metal particle solids (W/Hr./W) are suitable. In general, the higher the bed temperature or the lower the Conradson carbon content of the hydrocarbon liquid the higher the feed rate of liquid required to produce sufficient amounts of carbon in a form to bind the agglomerates together.

The total fluidizing gas velocity (including any gases liberated from the coking of the heavy hydrocarbons within the fluid bed) should be maintained within the superficial gas be used, however, defluidization of the bed may result. Conversely higher fluidizing gas velocities may be used, however excessive entrainment and loss of the 325 mesh particles may result.

BRIEF DESCRIPTION OF THE DRAWING The drawing illustrates a preferred embodiment of the invention wherein highly reduced iron ore particles are agglomerated in a fluidized solids bed using a heavy hydrocarbon liquid in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring specifically to the drawing, iron ore consisting essentially of hematite, F e is crushed and ground by conventional means to particle sizes essentially entirely within the range of l to 10,000 microns and averaging about 125 microns with over 20 percent finer than 325 mesh (44 microns). The finely ground ore is introduced via line 11 into a fluidized bed reactor 10 wherein it is fluidized and reduced by ascending reducing gases consisting of about 60 percent hydrogen and 40 percent carbon monoxide introduced via line 12. The ore is reduced in multiple stages (not shown) from Fe 0 to Fe 0 and then to FeO and finally to a product consisting of about 90 percent metallic Fe, about 5 percent FeO, with the remainder miscellaneous impurities or gangue constituents, such as calcium oxide and the like. After reduction the spent reducing gases are withdrawn from the reactor through outlet 13 and can be recovered by removing oxidized constituents, i.e. CO and H 0, and reused. The reduced finely divided product is withdrawn from reactor at line 21. The product consists of particles having the size ranges similar to that of the ore feed. Screen analysis shows that 21.1 weight percent of the reduced ore product is of particle sizes finer than 325 mesh. The particulate reduced ore product which is withdrawn from the reactor through line 21 is introduced directly into fluidized bed 22 of agglomerator 20. Fluidization is maintained by ascending fluidizing gas introduced through inlet 23. The fluidizing gas consists of recovered H and CO gas from reactor outlet 13, after regeneration by removal of CO and H 0, and is introduced at at rate to provide a superficial gas velocity of about 0.8 feet per second in the fluidized bed 22. A heavy hydrocarbon liquid, produced from conventional steam-cracking of tar, having an initial boiling point of 650 F. and having a Conradson carbon content of 34 weight percent (93 percent carbon) is introduced via line 24 and nozzles 26, 27, and 28 and sprayed onto the top of the fluidized bed 22. The nozzles are of conventional design, operated at relatively low, i.e., about l5 p.s.i.g., pressures and produce spray droplets predominantly above 200 microns in diameter. The heavy hydrocarbon liquid feed is preheated to 400 F. to lower its viscosity sufficiently for easy flowing and spraying.

An alternative procedure is to withdraw all or part of the reduced ore fines from reactor 10 with the gases in line 13, recover the fines, e.g., by scrubbing with the heavy hydrocarbon, and feed an intimately mixed blend of the fines and hydrocarbon through line 24 to the agglomerator 20. This insures good contacting and sticking between fines and hydrocarbon residue.

Exiting gases leave through line and contain both the fluidizing gas and the vapors liberated from the cracking and coking of the liquid hydrocarbon. The gases contain substantial quantities of light hydrocarbons which can be recovered as a product or, alternatively, the entire gas stream exiting through line 25 can be used in the iron ore reduction reactor 10 to reduce the oxides therein.

The residence time of the solids in the agglomerator 20 are controlled at between about 10 and 60 minutes, generally, to provide sufficient time for partial coking of the hydrocarbons and agglomeration of the particles to occur. It is found that in about 30 minutes holding time approximately 6 weight percent carbon is deposited at 900 to l,000 F. using the 34 weight percent Conradson carbon feed.

The coke-coated reduced iron product is withdrawn through line 30, cooled and stored for further use. It is found that the product contains only 0.6 weight percent of particles ranging less than 325 mesh in size. Thus, approximately 97 percent of the very fine particles greater than 325 mesh in SIZE.

Depending upon the temperature of the reduced ore fed to the agglomerator 20 through line 21, varying amounts of hydrocarbon can be coked without the addition of additional heat to the fluid bed 22. Thus, for example, when reduced ore product is withdrawn from the reduction reactor 10 and introduced into the agglomerator 20 at about l,475 F up to about 8 percent by weight of carbon can be deposited upon the ore without the addition of extraneous sources of heat.

The agglomerator 20 can be operated at any convenient pressures; superatmospheric pressures are preferred, however to minimize equipment size and gas rates and to make possible the use of lower carbon content hydrocarbons. Preferably, the agglomerator is used at pressures slightly above the pressure in reactor 10 so that exiting gasses from line 25 can be introduced directly into reactor 10.

It will be apparent to those skilled in the art that many variations can be made without departing from the spirit and scope of the invention.

What is claimed is:

l a process for making agglomerated of reduced iron ore particles comprising:

providing a fluidized bed of reduced iron ore particles;

introducing into said bed reduced iron ore particles containing substantial amounts of very fine particles less than about 325 mesh in size;

introducing into the bed droplets of heavy liquid hydrocarbon at rates ranging from about 0.l to about 10 part by weight of hydrocarbon per hour per part of metal particles in the bed, said hydrocarbon droplets ranging from about one-tenth the size of the largest particle for which agglomeration is d desired to about ten times the size of the average particle in the fluid bed and having Conradson carbon contents above about 10 weight percent; and, maintaining the particles within said bed at temperatures ranging from about 850 F. to about l,l00 F. for a time sufficient to partially crack said hydrocarbon and deposit coke on said very fine particles, whereby said very fine particles are cemented together with said coke and agglomerated to form particles larger than 325 mesh in size.

2. The process of claim 1 wherein said heavy liquid hydrocarbon contains at least about 20 weight percent Conradson carbon 3. The process of claim 1 wherein said bed of wherein said bed is fluidized with nonoxidizing gases at superficial gas velocities ranging from about 0.3 to about 1.5 ft./sec. 1.5

4. The process of claim 3 wherein said superficial gas velocities range from about 0.5 to about 1.0 ft./sec.

5. The process of claim 1 wherein said heavy liquid hydrocarbon is sprayed onto the top of said fluid bed.

6. The process of claim 1 wherein said particles are maintained within said bed at temperatures ranging from about 850 F. to about l,l00 F. for a residence time ranging from about 10 to about 60 minutes.

7. The process of claim 6 wherein said bed is maintained at temperatures ranging from about 900 F. to about l,00O F.

8. The process of claim I wherein said reduced iron ore particles containing substantial amount 5 of very fine particles less than about 325 mesh in size are obtained by recovering said particles from fluidized iron ore reduction process gases.

9. The process of claim 1 wherein said reduced iron ore particles containing substantial amounts of very fine particles and said heavy liquid hydrocarbon are introduced in admixture.

10. The process of claim 9 wherein fluidized iron ore reduction process gases are scrubbed with said heavy hydrocarbon whereby an admixture of said fines and hydrocarbon is provided. 

2. The process of claim 1 wherein said heavy liquid hydrocarbon contains at least about 20 weight percent Conradson carbon
 3. The process of claim 1 wherein said bed of wherein said bed is fluidized with nonoxidizing gases at superficial gas velocities ranging from about 0.3 to about 1.5 ft./sec. 1.5
 4. The process of claim 3 wherein said superficial gas velocities range from about 0.5 to about 1.0 ft./sec.
 5. The process of claim 1 wherein said heavy liquid hydrocarbon is sprayed onto the top of said fluid bed.
 6. The process of claim 1 wherein said particles are maintained within said bed at temperatures ranging from about 850* F. to about 1,100* F. for a residence time ranging from about 10 to about 60 minutes.
 7. The process of claim 6 wherein said bed is maintained at temperatures ranging from about 900* F. to about 1,000* F.
 8. The process of claim 1 wherein said reduced iron ore particles containing substantial amount s of very fine particles less than about 325 mesh in size are obtained by recovering said particles from fluidized iron ore reduction process gases.
 9. The process of claim 1 wherein said reduced iron ore particles containing substantial amounts of very fine particles and said heavy liquid hydrocarbon are introduced in admixture.
 10. The process of claim 9 wherein fluidized iron ore reduction process gases are scrubbed with said heavy hydrocarbon whereby an admixture of said fines and hydrocarbon is provided. 